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Explain concept of current leads or lags voltage by 90
Asked by rathod1234sujal | 15 Nov, 2022, 07:10: PM Expert Answer Let us consider an inductor of inductance L is connected across a AC voltage source as shown in figure.

Let the alternating voltage v across the voltage source is

ξ = vm sin(ω t )......................................(1)

where vm is peak voltage and ω is angular frequency .

Voltage across inductor is given as  L (dI/dt )

Hence we have , L (dI/dt ) = vm sin(ωt )

dI = ( vm / L ) sin(ωt )

Current through the inductor is determined by integrating above expression ................................(2)
where Lω is known inductive reactance

If we compare eqn.(1) and (2) , we see that phase of current lags by π/2 or quarter cycle
in comparision to the phase of voltage . This is illustrated in the figure given below --------------------------------------------------------------------------------------------------------------- Let us consider now , a capacitor is connected across the alternating voltage source.

Voltage across capacitor  , v = q /C

since current is rate of flow of charge , i = dq/dt  =  C ( dv/dt )

Using eqn.(1) , we get , ...........................(3)
where 1/(Cω) is capacitive reactance .

if we compare eqn.(1) and eqn.(3) , we see that phase of current leads by π/2 or one quarter of cycle .

This is illustrated in the figure given below Answered by Thiyagarajan K | 16 Nov, 2022, 05:45: PM
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